Electric field engineering and modulation of CuBr: a potential material for optoelectronic device applications

I–VII semiconductors, well-known for their strong luminescence in the visible region of the spectrum, have become promising for solid-state optoelectronics because inefficient light emission may be engineered/tailored by manipulating electronic bandgaps. Herein, we conclusively reveal electric-field-induced controlled engineering/modulation of structural, electronic and optical properties of CuBr via plane-wave basis set and pseudopotentials (pp) using generalized gradient approximation (GGA). We observed that the electric field (E) on CuBr causes enhancement (0.58 at 0.0 V Å−1, 1.58 at 0.05 V Å−1, 1.27 at −0.05 V Å−1, to 1.63 at 0.1 V Å−1 and −0.1 V Å−1, 280% increase) and triggers modulation (0.78 at 0.5 V Å−1) in the electronic bandgap, leading to a shift in behavior from semiconduction to conduction. Partial density of states (PDOS), charge density and electron localization function (ELF) reveal that electric field (E) causes a major shift and leads to Cu-1d, Br-2p, Cu-2s, Cu-3p, and Br-1s orbital contributions in valence and Cu-3p, Cu-2s and Br-2p, Cu-1d and Br-1s conduction bands. We observe the control/shift in chemical reactivity and electronic stability by tuning/tailoring the energy gap between the HOMO and LUMO states, such as an increase in the electric field from 0.0 V Å−1 → 0.05 V Å−1 → 0.1 V Å−1 causes an increase in energy gap (0.78 eV, 0.93 and 0.96 eV), leading to electronic stability and less chemical reactivity and vice versa for further increase in the electric field. Optical reflectivity, refractive index, extinction coefficient, and real and imaginary parts of dielectric and dielectric constants under the applied electric field confirm the controlled optoelectronic modulation. This study offers valuable insights into the fascinating photophysical properties of CuBr via an applied electric field and provides prospects for broad-ranging applications.


Introduction
Wide band gap semiconductors renowned for strong luminescence in the visible region of the spectrum produce high concentrations of excessive charge carriers and have become prospective materials for optoelectronic applications. [1][2][3] The majority of our daily lighting systems are based on InGaN optical emitters, 4,5 while, ZnO, 6 ZnS, 7 ZnTe 8 and ZnSe 9 frequently used in at panels and lasing applications suffer serious challenges. For example, the larger lattice mismatch with substrates, such as sapphire, Si, or SiC, direct to the intrinsic structural defects or distortions, such as mist dislocations, 10 stress in deposited lms, 11 in-phase (IPB) and out-ofphase grain boundaries (OPBs), 12 and secondary impurity phases 13 to the parent phases causes the hindrance in the light emitting efficiency of the devices. Additionally, excessive and continuous in use in household and luminescent optoelectronic devices causes scarcity, necessitating alternative novel materials with better or closer properties to in-based systems. 14,15 I-VII Cu halides (CuX; X = Cl, Br, I, etc.) are well thought-out potential materials to replace In-based optoelectronic systems because of their structural diversity, direct band gap (3.0-3.5 eV at 300 K), transparency throughout the visible region (above 420 nm), large binding, smaller bulk modulus, large ionicity, diamagnetic behavior, non-linear optics, large excitonic binding (around 100 to 110 meV) energies (in the UV/visible region), negative spin orbit and rich excitonic photophysical/ chemical optoelectronic properties (such as solid state lightening). [16][17][18] These compounds are tetrahedral-coordinated compound semiconductors that crystallize into the zinc blend lattice (space group F43m), where Cu atoms are located at (0, 0, 0) and halide (F, Cl, Br, and I) atoms are located at (1/4, 1/4, 1/4) positions transformed from zinc blend (B 3 ) to several intermediate low symmetry phases and rock salt (B 1 ) structure under application of higher pressure (usually in the region of the 10 GPa). 19 The lled d 10 -shell in addition to the s 2 p 6 rare-gas valence shell originate valence band results in a deep core level with almost no dispersion apart from the spin-orbit splitting, which is part of the uppermost valence band, resulting in signicant optoelectronic properties, as revealed recently that CuCl deposited on the Si substrate is a wideband gap (WBG) material compatible with the photoluminescence industry. 20, 21 Koch et al. 22 briey outlined the UV/vis emission spectral for copper-based halides and demonstrated that CuBr extends the probable range of blue hues in the recognized emitter wavelength range and have excellent lattice match with a substrate such as Si, resulting in fewer structural defects in the deposited CuBr lms via high vacuum [23][24][25] or chemical solutionbased deposition (CSD) process [26][27][28] and yield efficient roomtemperature free-excitonic emission. These materials have been widely produced, but no thorough theoretical investigations have been conducted on intrinsic and extrinsic electric eld modulation and controlled engineered optoelectronic, mechanical, dielectric, elastic and photocatalytic properties, which may massively affect the emission, and conduction can potentially be useful in the controlled miniaturized optoelectronic industry that requires thorough and comprehensive investigations.
Herein, we selected the CuBr compound, which is the rst ever thorough report of the electric eld modulation and engineering of the bandgap of CuBr with zinc blende cubic (a = 5.69 Å, b = 5.69 Å and c = 5.69 Å) sphalerite structure exhibiting F43m space group (where the Cu 1+ is bonded to four equivalent Br 1− atoms to form corner-sharing CuBr 4 tetrahedra; the Cu-Br bond lengths are 2.47 Å, and the Br 1− is bonded to four equivalent Cu 1+ atoms to form corner-sharing BrCu 4 tetrahedra) halides via plane-wave basis set and pseudopotentials (pp) using generalized gradient approximation (GGA) [32][33][34] in QUANTUM ESPRESSO. [35][36][37] Despite wide theoretical studies on semiconductors, very few studies are available on Cu-based halides to date. We rst ever thoroughly report the external electric eld modulation and engineering of the energy band gap and its effect on the structural, electronic and optical properties of CuBr, which may lead to potentially controlled novel miniaturized future optoelectronic and photoluminescence technology.

Results and discussions
The electronic band structure and density of states (DOS) provide information about the electronic properties of materials that may be modulated, controlled, and engineered upon the application of an external electric eld, offering a window of opportunity for potential utilization in micro/nanoelectronic technology. Fig. 1(a-i) shows the bandgap modulation and engineering for CuBr halides with (0.05 and without the application of an external electric eld (0.0 V Å −1 ) using GGA approximation. In the absence of an external applied electric eld (E) ( Fig. 1(a)), the top of the valence band maximum (VBM) and the bottom of the conduction band minimum (CBM) are not overlapping located and diverge at the G-G symmetry point of the Brillouin zone (BZ) responsible for the direct band gap, E g , (0.58 eV at 0.0 V Å −1 ), validating semiconducting behavior that is consistent with previously reported results. 17,19,20,41 The direct band gap at 0.0 V Å −1 appears owing to the main interaction between Cu metal d-states and Br p-states, which pull down valence bands near the Fermi level (E F ). It is clearly observed that the highest valence band (VB 1 and VB 2 ) states have d-state electron contributions, whereas the p-state electrons mainly contribute to the lowest (VB 3 ) bands. The band structures below the critical external eld (0.7 V Å −1 and −0.5 V Å −1 ) comprise the lower part, VB 1 , and at part VB 2 , appearing because of the hybridization of 3d Cu t2g + and 3p Br − orbital (VB 2 ) and 3p eg of 3d Cu + orbital (VB 2 ). The lower lying VB 3 band is mostly derived from the 3p (Br − ) orbital, whereas the s (Br − ) orbital coins the deeper VB 4 band entirely. The shapes of the lower VB 3 and VB 4 bands are the same for the zinc blende materials, in which the d bands are far away from the valence band region. Fig. 1(b-i) depicts that the application of an external electric eld (V Å −1 ) causes modulation and tuning in the valence and conduction band, resulting in a shi and widening of the direct bandgap at G symmetry point below the critical electric eld (0.05 V Å −1 E g = 1.58, −0.05 V Å −1 E g = 1.27 and 0.1 V Å −1 , E g = 1.63). The bandgap starts to shrink at 0.5 V Å −1 and −0.1 V Å −1 shis from 1.63 to 0.78 and 1.27 to 1.13; above the critical eld (0.7 V Å −1 and −0.5 V Å −1 ), conduction band crosses the Fermi energy level and overlaps valence band, resulting in a metallic response. The detailed computed values of the energy bandgap obtained as a function with and without an applied external electric eld (above and below the critical electric eld) for the CuBr system are listed in Table 1, conrming that CuBr responds sensitively and monotonously to the external applied electric eld (V Å −1 ).
The bandgap expanded and tuned from 0.58 (at 0.0 eV) to 1.63 (at 0.1 V Å −1 ) via applied external electric eld (V Å −1 ) as stimuli provide a window of opportunity to develop, control, engineer and modulate future optoelectronic devices, possibly causing strong luminescence in the visible region of the spectrum because of the large bandgap producing a high concentration of excessive charge carriers. No previous theoretical and experimental studies have been conducted on electric eld engineering and modulation of CuBr, and we believe this study will be used as a reference and has the potential for further investigation of the engineering, controlling and modulating of modern optoelectronic devices.
The total density of states (TDOS) and partial density of states (PDOS) for the CuBr compound are shown in Fig. 2(a-i), providing in-depth information about the role of orbital contribution and their effect on the bandgap modulation and engineering with and without an external applied electric eld (E). The dashed line between the valence band (VB) and conduction band (CB) represents the Fermi energy level. In the absence of an external electric eld (E = 0 V Å −1 ), the valence band is dominated by Cu-1d and Br-2p states, and there is less contribution from Cu-2s and Cu-3p orbitals near the Fermi energy levels (the dotted lines shown in Fig. 2a). However, in the case of the conduction band, the Cu-3p orbital contributes the maximum, while Cu-2s and Br-2p contribute less. There is a very insignicant contribution from Cu-1d and Br-1s orbitals. These results conrm that Cu-d and Br-p states mostly dominated the valence band, whereas in the conduction band (CB), the s and d states of CuBr are rarely involved. The direct bandgap starts to widen with the utilization of an external applied electric eld, and upon the application of 0.05 V Å −1 and 0.1 V Å −1 , the bandgap increases from 0.58 to 1.58 and 1.63. The increase in band gap at 0.05 V Å −1 and 0.1 V Å −1 may be caused mainly by the interactions and orientation of electron orbital states; the Cu-1d and Br-2p states have major contributions, Cu-2s and Cu-3p states have less contribution, and Br-1s has an insignicant contribution in the valence band. However, in conduction bands, Cu-3p, Cu-2s and Br-2p orbitals have the main contribution and Cu-1d and Br-1s have less contribution. The increase in bandgap upon application of electric eld (E) as external stimuli at 0.05 V Å −1 and 0.1 V Å −1 implies that more electron excitation energies are required from the valence to the conduction band; henceforth, the light of a higher frequency and shorter wavelength would be absorbed. The external electric eld (0.1 V Å −1 and 0.5 V Å −1 ) causes electron energy excitation to the electrons present at lower energy levels with the main contribution of Cu-3p states at E = 0.0 V Å −1 in conduction band shi to the Cu-3p, Cu-2s and small contribution in the same energy range from Br-2p. This indicates that the Cu-2s (main contribution) and Br-2p interplay a major role, causing an increase in bandgap depending on the contribution of electrons of the same or different spin states and crystal eld causing repulsion or attraction may lead to widening bandgap upon the external electric eld. However, upon a further increase in the applied electric eld (E) to 0.5 V Å −1 , we observed that all the energy bands started to expand, and the bandgap exhibited a sharp decrease from 1.63 eV to 0.78 eV, depicting the start of the transition from the semiconductor to metallic behavior.
This decrease in bandgap generated by orbital orientations and interactions is conrmed; Fig. 2(a-i) shows that the valence band is formed because of the distinct hybridization of Cu-1d and Br-2p orbitals with less contribution from Cu-2s, Cu-3p, and Br-1s orbitals. However, in the conduction bands, Cu-3p, Cu-2s and Br-2p orbitals have the main contribution and Cu-1d and Br-1s have less contribution. In all these processes of electric eld modulation, tuning the bandgap of CuBr remains direct at the G-G symmetry point of the Brillouin zone. However, on further increase in the electric eld to 0.7 V Å −1 , −0.5 V Å −1 the valence band crosses the Fermi energy level, vanishing the bandgap, and CuBr turned into metallic from a semiconductor. Interestingly, the applied electric eld initially causes an increase in bandgap from 0.58 eV to 1.63, decreases the direct bandgap at the G-G symmetry point of the Brillouin zone from 1.63 eV to 0.78 and then overlaps conduction and valence band at E = 0.7 V Å −1 and −0.5 V Å −1 . Fig. 3(a-i) depicts the effect of the applied electric eld (E) on the engineering and modulation of the highest occupied molecular orbitals (HOMO) or bonding orbitals and lowest unoccupied molecular orbitals (LUMO) or anti-bonding orbital energy wave functions.
In CuBr compounds, the HOMO orbitals help Cu and Br to form CuBr bonds, which are naturally lower in energy than the LUMO orbitals that cleave the bonds between Cu and Br. To achieve lower energy stable states for CuBr, the Cu electrons interact with Br electrons to form CuBr bonding. The energy difference between HOMO and LUMO states demonstrates the ability of electrons to jump from occupied to unoccupied orbitals, demonstrating the ability of the molecular orbital to participate in chemical reactions. The energy gap (DE) between the HOMO and LUMO orbitals (which is the difference between the energies of HOMO and LUMO states (E LUMO -E LOMO )) represents the chemical activity, and a shorter gap corresponds to stronger chemical activity, as illustrated in Fig. 3(a-i), and their values are listed in Table 1. In the absence of an applied electric eld (E) at 0.00 V Å −1 , the energy gap (DE) between the HOMO and LUMO states of CuBr is 0.78 eV. However, there is a tendency of a shi in increase and decrease in energy gap via applied electric eld (E), which may demonstrate the controlled tailored ability of chemical reactivity and electronic stability of CuBr. It is obvious from Fig. 3(a-i) that upon the increase in the electric eld from 0.0 V Å −1 / 0.05 V Å −1 / 0.1 V Å −1 , there is an increase in the energy gap (DE) from 0.78 eV to 0.961 eV, indicating more electronic stability and less chemical reactivity. However, the converse is the case upon a further increase in the electric eld to 0.5 V Å −1 , in which the HOMO and LUMO energy gaps shrink to −0.643 eV, demonstrating that electronic instability and high chemical reactivity conrm a major shi in response, which agrees well with the modulation of bandgap and PDOS calculations. The values of LUMO, HOMO energies and the energy gap between LUMO and HUMO energy levels are listed in Table 1. We observed that the overall shapes of the HOMO and LUMO energy states also changed ( Fig. 3(a-i)). This is because Table 1 Detailed values of the electric-field-induced electronic bandgap and engineering and modulating of the highest occupied molecular orbitals (HOMO) or bonding orbitals and lowest un-occupied molecular orbitals (LUMO) or anti-bonding orbital energy wave function properties of CuBr  the electric eld (E) causes a shi in the interaction of various orbitals, such as Cu-1d, Cu-2s, Cu-3p, Br-1s and Br-2p. The interaction between metallic Cu and halide Br in CuBr with and without an applied electric eld (E) causing the change in charge transfer and hybridization is explored by electronic charge density distribution calculations, which is widely accepted for predicting charge density. Fig. 4(a-g) and 5(a-g) illustrate the electric eld modulation of charge density distribution in CuBr in 3D 2 × 2 × 2 extended boundary unit cells and primitive unit cells.
We evaluated several patterns under various applied electric elds (0.00 V Å −1 , 0.05 V Å −1 , 0.1 V Å −1 , 0.5 V Å −1 , −0.05 V Å −1 , −0.1 V Å −1 , and −0.5 V Å −1 ) of the calculated charge density to validate the electronic modulation and tunability. It is evident that charges accumulate and share between the Cu metal and halide Br atoms, indicating the existence of directional shared bonding upon the application of an electric eld (E). The sharing of mutual cations and anions shows that covalent and charge transfer reveal an ionic bonding nature. It is clear from Fig. 4(a-g) and 5(a-g) that below the applied critical external eld (0.7 V Å −1 and −0.5 V Å −1 ), CuBr displays charge sharing and covalent bonding among the anion-anion (Br-Br) and anion-cation (Cu-Br) atoms.
However, the charge density distribution changes upon the application of a higher electric eld (0.5 V Å −1 and −0.5 V Å −1 ), validating the shi in the nature of CuBr from semiconducting to metallic. In the absence of a eld at 0.0 V Å −1 , the charge distribution is more around the Br atoms whereas less around the Cu atoms. We observed an evident shi in charge distribution upon the eld; for example, at 0.05 V Å −1 , the charge density starts to transfer from Br to Cu atoms. The charge distribution somehow demonstrates a shi in behavior from semiconductor to metallic at higher elds of 0.5 V Å −1 and −0.5 V Å −1 .
To understand the role of the electric eld in the bonding patterns, we performed electron localization function (ELF) calculations, which provide insight into (local) the distribution of electrons. Fig. 6(a-i) depicts the front view of the computed ELF with and without an applied electric eld.
The colored regions around the Cu (red) and Br (purple) atoms represent the range (high or less) of electron localized density. In the absence of an applied electric eld (0/0 V Å −1 ), high charge density is observed in neighboring Br atoms, which may be attributed to the presence of strong s bonding. However, the applied electric eld (E) results in charge transfer or accumulation from Br atoms onto Cu atoms. We observed that Cu atoms are responsible for the low charge density although the electric eld causes modulation, accumulation and transfer, in which the low charge density may be due to the weakening of the s bonding between the Cu atoms and the neighboring Br atoms.
We have investigated the optical properties of CuBr, including the optical reectivity R(u), refractive index (n(u)), extinction coefficient k(u), real 3 1 (u) and imaginary 3 2 (u) parts of dielectric and dielectric constants 3(u) for the various energy ranges under the applied electric eld using GGA techniques. Fig. 7(a-d) shows the real 3 1 (u) and imaginary parts of the dielectric constant 3 2 (u) for CuBr with respect to the applied external electric eld above and below the critical external electric eld (E C ) as a function of energy (eV).  Table 2. It is clear from Fig. 7(a and b) that in the absence of an applied electric eld, the 3 1 (u) Fig. 4 (a-g) Electric field-induced engineering and modulation of the charge density distribution in the 3D extended 2 × 2 × 2 CuBr boundary unit cells calculated using the GGA scheme.
increases as the energy increases. The magnitude of the peak of the real dielectric decreases as the applied electric eld (up to 0.1 V Å −1 and −0.1 V Å −1 ) increases, suggesting an increase in the band gap. There is a sharp increase in 3 1 (u) as the electric eld increases from 0.1 V Å −1 to 0.5 V Å −1 because the bandgap decreases, demonstrating the behavior shi from semiconducting to conducting with the applied eld. Fig. 7(c and d) illustrates the imaginary part of the dielectric constant 3 2 (u)as a function of the given photon energy (eV) above and below the critical applied electric eld (0. for the CuBr system. To explore excitons, we must consider the imaginary part of dielectric 3 2 (u) because it contains a signature of exciton energies. Imaginary dielectrics 3 2 (u) represent four major peaks in the energy ranges 3.8-4.1 eV, 4-4.4 eV, 5.7-6.0 eV, and 9.5-10 eV for the CuBr system at 0.0 V Å −1 , corresponding to the four absorptions. The imaginary dielectric absorption peaks decrease as the applied external eld increases and reach a minimum value above the critical eld (0.5 V Å −1 ). It is noteworthy that the absorption peak shis from lower energy to higher energy with the utilization of an external applied eld. Furthermore, the sharpness of the absorption peak increases as the electric eld increases. Few absorption peaks exhibit an increase in width, which could be due to the mixed transition. The major contributions to the optical transition at low eld (0.0 V Å −1 , 0.05 V Å −1 , −0.05 V Å −1 , 0.1 V Å −1 and −0.1 V Å −1 ) belong to the Cu-d and Br-p states. However, at the higher eld (0.5 V Å −1 , −0.5 V Å −1 , 0.7 V Å −1 and −0.7 V Å −1 ), the major contribution shis to the s-p-d states.
The shi of absorption edge towards the higher energies with applied external electric eld (at 0.5 V Å −1 , 0.7 V Å −1 and −0.5 V Å −1 and above) illustrates a reduction in bandgap, as shown in Fig. 7(a-d). The optical absorption edge occurs at the G point of the Brillouin zone (BZ) between the conduction and valence bands, demonstrating a threshold for direct optical transition. The interesting fact to notice here is that 3 2 (u) decreases as the positive applied electric eld increases and even modulates over the negative applied electric eld. This is because with an applied electric eld, CuBr becomes polarized, but the eld produced due to the polarization of the CuBr minimizes the effect of the external eld. These results indicate that the dielectric response of CuBr with an applied electric eld (E) conrms its potential usage in controlled optoelectronics. Maximum energy loss functions above and below the critical eld with the negative eld are demonstrated in Fig. 7(e and f), which are conned to the energy regions where the electrons are not typically restricted to their lattice site and execute oscillation upon light exposure. It is obvious that the maximum energy loss function (ELS) minimum value refers to the higher value of the imaginary part of the dielectric, depending on the energy band gap, which varies with the applied external electric eld. For example, the maximum energy loss function increases as the band gap decreases with the application of a higher eld, resulting in a transition from semiconducting to a metallic behavior.
The complex refractive index (ñ) is a crucial optical property of material given by the following formula: 44,45 where n represents the real refractive index and k represents the attenuation index or extinction coefficient. We evaluate both n and k for CuBr by utilizing the imaginary part of the dielectric function using the following equation: 44,45 nðuÞ ¼ 1 ffiffi ffi 2 p The calculated values of the refractive index n(u) and extinction coefficient k(u) as a function of the given photon energy (eV) above and below the critical applied electric eld (0.00 V ) for the CuBr system are shown in Fig. 8(a-d) and listed in Table 3. The refractive index n(u) increases as the band gap decreases upon the utilization of the applied external electric eld, reaching the maximum value at the critical eld (3.8 at 0.7 V Å −1 and 5.8 at −0.7 V Å −1 ) and following the trend of the real part of dielectric 3 1 (u) that conrms semiconducting to metallic band transition. Fig. 8(c) demonstrates that the optical reectivity spectra with respect to the applied electric eld at given phonon energies provide basic information about various critical points of transition. We extracted the electric eld tailored, manipulated and controlled optical reectivity for CuBr below, above and in a negative polarization applied electric eld using the fundamental relation: 46 The complex refractive index n(u) demonstrates an optical response to electromagnetic waves or light in two major parts: the refractive index, n(u), and extinction coefficient, k(u). These are energy and frequency dependent parameters, respectively.
The optical reectivity R(u) with and without an applied electric eld for the CuBr system is calculated and represented in Fig. 8(c). We observed that optical reectivity decreases and shis toward lower values as the applied electric eld increases. Such a shi and decrease in optical reectivity R(u) with a higher applied eld (E) conrm the transformation from semiconducting CuBr to metallic. The maximum optical reectivity R(u) values at zero photon energy (0 eV) are associated with the highest absorption energy. Table 2 Detailed individual and average values of electric-field-induced real part of dielectric 3 1 (u), imaginary part of dielectric 3 2 (u) and dielectric constant 3(u) of CuBr

S. no
Electric eld (V Å −1 ) 1 st peak 2 nd peak 3 rd peak 4 th peak 5 th peak Avg imaginary Average real Dielectric const

Conclusions
In summary, we rst successfully reported the effect of the external applied electric eld (E) on electronic bandgap engineering and modulation, causing changes and shis in structural, electronic and optoelectronic properties of CuBr via plane-wave basis set and pseudopotentials (pp) using the generalized gradient approximation (GGA) based on density functional theory (DFT). We observed that when the external electric eld was applied, there was a signicant increase in the bandgap, such as from 0.58 at 0.0 V Å −1 to 1.63 at 0.1 V Å −1 (about 280% increase). This modulation in the electronic bandgap via the applied electric eld (E) results in a behavioral shi from semiconducting to metallic. The partial density of states (PDOS), charge density and electron localization function (ELF) calculations reveal that the applied electric eld (E) modulates the orbital contribution and leads to the main contribution of Cu-1d, Br-2p, Cu-2s, Cu-3p, and Br-1s orbitals in the valence band and Cu-3p, Cu-2s and Br-2p, Cu-1d and Br-1s orbitals in the conduction band, signicantly conrming the controlled optoelectronic properties. Additionally, we found that the chemical reactivity and electronic stability of CuBr may be controlled by tuning and tailoring shis in HOMO and LUMO states with an increase or decrease in gap via an applied electric eld (E). The increase in the electric eld from 0.0 V Å −1 / 0.05 V Å −1 / 0.1 V Å −1 causes the increase in the energy gap to lead to electronic stability and less chemical reactivity. However, the converse is the case upon a further increase in the electric eld to 0.5 V Å −1 , where the gap shrinks to 0.78, leading to electronic instability and high chemical reactivity that indicate a major shi in response. This is further conrmed by observing modulation in the bandgap and PDOS calculations. Optical properties, such as optical reectivity R(u), refractive index (n(u)), extinction coefficient k(u), real 3 1 (u) and imaginary 3 2 (u) parts of dielectric and dielectric constant 3 1 (u) for various energies ranging in eV under the applied electric eld, conrm the controlled optoelectronic response in CuBr. This work offers valuable insights and an in-depth study of the fascinating photophysical properties of CuBr lms via an applied electric eld, and it will open a prospect to their utilization in various applications.

Conflicts of interest
I hereby conrm that the work reported in this manuscript is novel and has no conict of interest.

Data availability
The raw/processed data required to reproduce these ndings cannot be shared at this time as the data also forms part of an ongoing study. Furthermore, the data may be provided on request. Table 3 Detailed individual and average values of electric-field-induced the refractive index n(u), extinction coefficient k(u) and optical reflectivity R(u) of CuBr S. no. E (V Å −1 ) k 1st (u) k 2nd (u) k 3rd (u) k 4th (u) k 5th (u) k avg (u) n avg (u) R avg (u)